The present invention generally relates to heat exchangers and, more particularly, relates to a heat exchanger having heat transfer elements with improved heat transfer characteristics.
Conventional heat exchangers of the plate fin-tube type generally include of a plurality of parallel tubes having a plurality of perpendicular fins. The plurality of perpendicular fins is thermally coupled to the plurality of parallel tubes to serve as an evaporator. Heat absorbing fluid is forced through a capillary tube into the plurality of parallel tubes at a low temperature and pressure. Subsequent evaporation of the fluid removes heat energy from the air passing adjacent the tubes of the evaporator, thus cooling the air. The fins attached to the tube increase the effective heat absorbing area over which the airflow is directed, thus increasing the cooling efficiency of the evaporator. A small motor driven fan is utilized to draw air over the heat absorbing area of the evaporator and discharge the cooled air into the interior of the refrigerator.
Several attempts have been made to increase the cooling efficiency of the evaporator by varying the arrangement of the tube pattern and fin shape. U.S. Pat. No. 4,580,623 discloses a heat exchanger having parallel rows of serpentine tube coils slanting in the same direction and using ultra thin fins having a pattern embossed thereon to induce turbulence in the airflow over the evaporator. However, the refrigeration industry is currently requiring a wider evaporator to increase the face area of the evaporator met by the airflow to reduce the effects of frost growth and thereby increase the cooling efficiency of the refrigerator system. To enhance the cooling efficiency it is possible to add additional rows of tubes or additional fins to the evaporator. However, additional fins generally cause a narrowing of the space between fins, which may limit airflow there between and increase the amount of material necessary to manufacture the evaporator, thus increasing cost. Further, additional rows of fins may also lead to excessive air-pressure drops across the fins, especially as frost accumulates on the fins and tubes.
A need to improve the cooling efficiency of the current fin design is particularly felt in the area of xe2x80x9cdog-bonexe2x80x9d type heat exchangers. Dog-bone type heat exchangers generally include a plurality of fins each having a series of slots formed therein. These slots are generally in the shape of a dog bonexe2x80x94having generally circular end portions and a slightly narrower intermediate, connecting portion. Unlike other heat exchanger types, dog-bone heat exchangers employ a single, continuous tube that is bent into a serpentine-like pattern, which traverse back and forth through the series of slots formed in the fins once assembled. This single, continuous tube eliminates the need for complicated tube assembly, such as assembly and brazing of joints. The tube is bent into its preferred shaped prior to insertion through the dog-bone slots. Due to the narrower immediate portion of the dog-bone slots, the bends along at least one side of the final tube shape are crimped to enable insertion of the tube into the fins. This tube bundle is then inserted through the dog-bone slots to form the assembly. Traditionally, it is difficult to hold the fins in proper position during this insertion stage. Experience has shown that this difficulty is compounded if an irregularly shaped fin is used.
Dog-bone type heat exchangers are often used in refrigeration applications, such as refrigerator-freezer applications. Refrigeration applications typically use a lower airflow rate relative to commercial cooling systems. These lower airflow rates decrease the cooling capacity of the heat exchanger. Moreover, such refrigerator-freezer applications further require that frost be able to collect on the fins and tubes. Therefore, to minimize the chance of the fins being clogged with frost, the fins must be placed further apart to allow air to continue to pass through the evaporator as the frost accumulates. This increase separation of the fins limits the number of fins used and, furthermore, reduces the mixing of the airflow around the fins, thereby reducing the cooling capacity of the system. However, irregularly shaped fins are difficult to assemble with the continuous tube.
Accordingly, there exists a need in the relevant art to provide a dog-bone type heat exchanger system having evaporator fins that permit the accumulation of frost and the pass through of air, yet provides improved cooling capacity. Furthermore, there exists a need in the, relevant art to provide a dog-bone type heat exchanger having sufficiently spaced fins that provides improved mixing of the airflow around such fins to improve cooling capacity. Still further, there exists a need in the relevant art to provide a dog-bone type heat exchanger system having fins capable of improving the mixing of the airflow around such fins without adversely affecting the ease of assembly. Lastly, there exists a need in the relevant art to provide a dog-bone type heat exchanger system that overcomes the disadvantages of the prior art.
According to the principles of the present invention, a dog-bone type heat exchanger is provided having an advantageous construction and method of assembly. The dog-bone type heat exchanger includes a plurality of fin members for dissipating heat. Each of the plurality of fin members includes a pair of offset surfaces interconnected by a sloped interconnecting surface. The plurality of fins members may be spaced apart at a distance that is less than, equal to, or more than the offset distance between the pair of offset surfaces on each fin member.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.